Heat transfer fluids are known in the art to be used in heating and cooling systems; typically, said heat transfer media include water, aqueous brines, alcohols, glycols, ammonia, hydrocarbons, ethers and various halogen derivatives of these materials, such as chlorofluorocarbons (CFCs), hydrochlorofluorocarbons (HFCs), (per)fluorinated polyethers (PFPEs) and the like.
Such fluids are used to transfer heat from one body to another, typically from a heat source (e.g., a vehicle engine, a boiler, a computer chip or a refrigerator) to a heat sink so as to effect cooling of the heat source, heating of the heat sink or to remove unwanted heat generated by the heat source. The heat transfer medium provides a thermal path between the heat source and the heat sink; it may be circulated through a loop system or other flow system to improve heat flow or it can be in direct contact with heat source and heat sink.
Fluorinated fluids, thanks to their high chemical and thermal stability, non toxicity and non flammability, are particularly suited for applications in heat transfer circuits where such properties, in particular the non flammability, are extremely important due to high safety standards; examples thereof are cooling circuits on board of aircrafts, refrigeration systems for supermarkets or heat transfer circuits in industrial plants.
In particular, fluorinated ether fluids like, notably, (hydro)fluoro(poly)ethers are broadly used as heat transfer media due to their wide liquid range, especially for applications as low temperature secondary refrigerants for use in secondary loop refrigeration systems where the viscosity of the fluid should not be too high at the operating temperatures.
Thus, US 2007/0187639 (E. I. DU PONT DE NEMOURS & CO) 16 Aug. 2007 discloses a heat-transfer fluid composition including a heat-transfer fluid selected from saturated and unsaturated fluorocarbons, hydrochlorofluorocarbons, (hydro)fluoroethers, hydrocarbons, carbon dioxide, dimethyl ether, ammonia and mixtures thereof and a perfluoropolyether. The two end groups of said perfluoropolyether can be independently functionalized or unfunctionalized: a typical functional end group is selected from esters, hydroxyls, amines, amides, cyanos, carboxylic acids and sulfonic acids.
Also, WO 2007/099055 (SOLVAY SOLEXIS S.P.A.) 7 Sep. 2007 discloses use as heat transfer fluids of compositions comprising hydrofluoropolyethers (HFPEs) and/or hydrofluoroethers (HFEs) in combination with a (per)fluoropolyether having end-groups selected from pyridine, ammine, aryl classes. No data are provided regarding heat transfer properties of said compositions.
However, heat transfer media of the prior art generally suffer from the disadvantage that they do not suitably protect against corrosion heat exchange surfaces which are generally made of metal materials, such as, e.g., copper, iron, steel, aluminium. Cooling circuits are indeed typically exposed to leaks in proximity to the joint seals or filler lines: thereby, when thermal cycles are performed, moisture can penetrate therein and promote corrosion of metal heat exchange surfaces.
Further, there is a continuous need of heat transfer media having improved thermal conductivity so as to reduce heat exchange surfaces of the heat exchange system and therefore size and weight of such system, thus optimizing the available useful space; this size reduction/miniaturization is particularly advantageous especially on board of aircrafts, wherein space availability can be an issue.
There thus remain a need in the art for a heat transfer medium having improved thermal conductivity while exhibiting outstanding anti-rust properties, said medium being thus suitable for being used in heat transfer circuits generally made of metal materials, in particular lightweight materials such as aluminium, aluminium/magnesium alloys, titanium for applications in aircrafts and vehicles in general, and thus enabling overcoming drawbacks of heat transfer fluids of the prior art.